These ISO test shots were taken indoors using low-level diffuse natural daylight, auto white balance and program exposure. Checkmate, I think.
1/5th sec, F4.0, ISO 80
At the lowest ISO setting the image is smooth as silk, with perfect exposure and colour rendition. Unsurprisingly at this setting there is no image noise.
1/6h sec, F4.0, ISO 10
There is no visible difference between this 100 ISO shot and the previous one.
1/13th sec, F4.0, ISO 200
At 200 ISO there is a tiny amount of colour speckling in the darker areas, but there is still plenty of detail and the overall colour rendition remains accurate.
1/25th sec, F4.0, ISO 400
There is little difference between this 400 ISO shot and the 200 ISO version. The colour speckling is a little more pronounced, but noise is well controlled and the picture is quite printable.
1/50th sec, F4.0, ISO 800
At the highest ISO setting the image is now quite noisy and would not make a good print, although the overall colour balance is still quite accurate. This is about as good as most other cameras on 400 ISO.